Molecular dynamics insights into the structure, function, and substrate binding mechanism of mucin desulfating sulfatase of gut microbe Bacteroides fragilis.

The complex and dynamic consortia of microbiota that harbors the human gastrointestinal tract contributes ominously to the maintenance of health, the onset and progression of diverse spectrum of disorders. The capability of these enteric microbes to bloom within the gut mucosal milieu is often associated to the glycan metabolism of mucin-degrading bacteria. Accruing evidences suggests that the desulfation of mucin is a rate-limiting step in mucin degradation mechanism by colonic bacterial mucin-desulfating sulfatase enzymes (MDS) enzymes. Till date no experimental evidence is available on how conformational flexibility influences structure and substrate specificity by MDS of gut microbe Bacteroides fragilis. Henceforth, to gain deep insights into the missing but very imperative mechanism, we performed a comprehensive molecular dynamics study, principal component analysis and MM/PBSA binding free energies to gain insights into (i) the domain architecture and mode of substrate binding (ii) conformational dynamics and flexibility that influence the orientation of substrate, (iii) energetic contribution that plays very decisive role to the overall negative binding free energy and stabilities of the complexes (iv) critical residues of active site which influence binding and aid in substrate recognition. This is the first ever report, depicting the molecular basis of recognition of substrates and provides insights into the mode of catalysis by mucin desulfating sulfatase enzymes in gut microbiota. Overall, our study shed new insights into the unmapped molecular mechanisms underlying the recognition of various substrates by mucin desulfating sulfatase, which could be of great relevance in therapeutic implications in human gut microbiota associated disorders.